Mac: implement orientation/motion shared memory data fetcher.

content/browser/device_orientation/data_fetcher_shared_memory_base.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_SHARED_MEMORY_BASE_H_
 #define CONTENT_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_SHARED_MEMORY_BASE_H_
 
 #include <map>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 41 matching lines @@
   base::MessageLoop* GetPollingMessageLoop() const;
 
   // If IsPolling() is true this method is called from the |polling_thread_|
   // at regular intervals.
   virtual void Fetch(unsigned consumer_bitmask);
 
   // Returns true if this fetcher needs to use a polling thread to
   // fetch the sensor data.
   virtual bool IsPolling() const;
 
-  // Start() method should call InitSharedMemoryBuffer() and cache the obtained
-  // pointer for efficienty and thread-safety.
+  // Start() method should call InitSharedMemoryBuffer() to get the shared
+  // memory pointer. If IsPolling() is true both Start() and Stop() methods
+  // are called from the |polling_thread_|.
   virtual bool Start(ConsumerType consumer_type) = 0;
   virtual bool Stop(ConsumerType consumer_type) = 0;
 
  private:
   bool InitAndStartPollingThreadIfNecessary();
   base::SharedMemory* InitSharedMemory(ConsumerType consumer_type,
       size_t buffer_size);
 
   unsigned started_consumers_;
 
   scoped_ptr<PollingThread> polling_thread_;
 
   // Owning pointers. Objects in the map are deleted in dtor.
   typedef std::map<ConsumerType, base::SharedMemory*> SharedMemoryMap;
   SharedMemoryMap shared_memory_map_;
 
   DISALLOW_COPY_AND_ASSIGN(DataFetcherSharedMemoryBase);
 };
 
 }
 
 #endif  // CONTENT_BROWSER_DEVICE_ORIENTATION_DATA_FETCHER_SHARED_MEMORY_BASE_H_